As a well-known ground improvement method, heretofore it has been customary to inject self-hardening grout into ground to increase the degree of consolidation in the ground for ground reinforcement. As the grout, in addition to instantaneously-hardened grout characterized by short gelation time, slowly-hardened grout characterized by long gelation time is used.
As a ground improvement method aimed at restoring a building construction which has undergone uneven settlement due to earthquake or excavating work in a nearby area, there is proposed a technology to inject grout into that part of ground where building settlement has occurred to form a solidified support layer in the ground, so that the building construction, including its foundation, as a whole can be lifted up under a reaction force resulting from the layer formation (refer to Patent Literature 1, for example).
On the other hand, as a ground improvement method aimed at achieving ground reinforcement or water shutoff for, for example, soft ground, there is proposed a technology to control the rate of grout injection, grout injection pressure, selection between start and stop of grout injection, etc. for each of a large number of grout injection points on an individual basis to cope with the difference in soil conditions (coefficient of water permeability, porosity, etc.) between geological layers (refer to Patent Literatures 2 and 3, for example).
By way of another example of ground improvement methods, there is known a technology to form a columnar solidified support portion in ground by directing a jet of grout into a vertical hole formed in the ground by excavation (refer to Patent Literature 4, for example).